1. Field of Invention
The invention relates to a micro-electro-mechanical system (MEMS) package technology. More particularly, the invention relates to a MEMS package, such as the MEMS microphone capable of being chip-size scale.
2. Description of Related Art
MEMS microphone has been popular gradually due to the excellent features comparing to the conventional ECM microphone. The features of MEMS microphone includes: 1. thin and small size. 2. SMD (surface mountable device) indicating easy assembly with sold flow. 3. high stability and environmental resistance. However, in comparison with the IC package, the requirements of microphone package include receiving the sound pressure from acoustic signal, inducing mechanical motion and transferring to electrical signal. Therefore it needs an acoustic path to receive the sound pressure, a transducer to response the sound pressure, a sufficient back volume for transducer to reduce the damping coefficient and a good shielding to protect it from EMI. Currently, the most popular package is that the transducer is mounted on PCB and electrically couple to such PCB, and the conductive housing with an aperture is attached to the PCB enclosing the transducer. (FIG. 1) However, in such a way, the back volume of a transducer is only decided by the volume of the cavity of a transducer, indicating a small back volume and high damping coefficient to degrade the microphone performance.
Currently, most transducers have two chips in the package. One is the pure MEMS devices; the other is sensing IC. The drawbacks are: 1. large package size, 2. parasitic effect for the electrical connection between IC and MEMS devices. 3. high cost for extra sensing IC. It is inevitably intended for the miniature package size and low cost. Moreover, CSP (chip scale package) and wafer level package becomes more popular due to high electrical performance, small package size (as small as the chip size) and low cost. Such two chips in one package is not suitable to such CSP or WLP process. By the way, the size of a package mentioned above is also always larger than that of the transducer because the transducer has to be enclosed in the package.
FIG. 1 is a cross-sectional view, schematically illustrating a structure of conventional MEMS microphone. In FIG. 1, the conventional MEMS microphone includes a substrate 100. A MEMS microphone device 104, serving as a transducer, is formed on the substrate 100. MEMS microphone device 104 has a cavity 102 and a diaphragm over the cavity, allowing the diaphragm to vibrate with the acoustic sound. An integrate circuit (IC) 106 is also formed on the substrate 100. The bonding wire is used for the electric connection, so that the MEMS microphone device 104 is connected with the IC 106 for operation. Usually, the MEMS microphone package also needs a cover 108 to protect the MEMS microphone device 104 and the IC 106. In order to sense the acoustic sound from the environment, an aperture 110 is made to receive the acoustic sound. However, since the volume of the cavity 102 of the MEMS microphone device 104 is small. The sensitivity is insufficient.
How to design a MEMS microphone with more sensitivity or even in chip-size scale is still under development.